Optical systems, such as spectrometers and lux meters, have been widely used in numerous industries, including: biotechnology, environmental technology, electronics, food and beverage, industrial chemicals, materials, and pharmaceuticals. With the development of optoelectronics, the trend is to miniaturize the sizes of optical systems. Conventional optical systems that are commonly used in a laboratory setting tend to be easily damaged and need frequent calibration. The miniaturization of optical systems, on the other hand, enables the utilization of optical systems outside of the laboratory as portable test instruments. These miniaturized optical systems are suitable for a variety of innovative applications, including testing of blood, urine, pesticide residues, water quality, UV intensity, fruit sweetness, air quality, color difference between materials, and quality of optoelectronic products, as well as counterfeit alcohol, counterfeit money, counterfeit drugs, and jewelry detection, etc. These applications cover almost all areas of life and industrial fields, including home, outdoors, field surveys, onsite inspection, and material inspection in production lines.
An optical system typically includes an optical head for collecting scattered light and a light detector for measuring the intensity of the scattered light that are collected by the optical head. In lux meters, a photo sensor is adapted as the light detector. In spectrometers, the light detector includes a grating that separates complex light components into a diffracted light and a photo sensor that converts the disperse light to an electrical signal for further analysis. Given that the amount of light collected by the optical head may affect the sensitivity of the optical system, a more efficient optical head is needed. Currently, in most of the optical heads, cosine correctors are used. However, although substantially the same transmittance for light rays incident on the optical head at different angles may be achieved, the cosine corrector is not effective in increasing the amount of incident light that can be transmitted to the light detector.